General characteristics of horsetails. Equisetaceae department general characteristics and significance What structure does a horsetail spore have?
Division Equisetae. About 20-30 modern species of horsetails are known. These plants grow on our planet everywhere in areas with different climatic conditions - from Antarctica to Africa. But in North America and Eurasia, in the temperate and arctic zones, the greatest species diversity of horsetails is observed. This plant received the name “horsetail” for its external resemblance to the tails of animals, in particular horses. Horsetails grow in forests, meadows, swampy areas, and near water bodies.
All modern species of horsetail are perennial herbaceous plants with dense stems impregnated with silica, reaching an average height of 1 to 12 m. The largest species is the giant horsetail, found in tropical and subtropical forests with high humidity. Its length can reach 10-12 m. A characteristic feature of all types of horsetail is the presence of stem metamerism, that is, the correct alternation of nodes and internodes. Horsetails have small, scale-like leaves arranged in whorls at the nodes. Lateral branches also form at the nodes of the stem. Photosynthesis occurs in the tissue of green stems and branches, the surface of which is further increased by ribbing. The sporangia are located on hexagonal corymbose sporangiophores connected into apical strobili.
The underground part of horsetails is a branched powerful rhizome, in the nodes of which adventitious roots are formed. Some species of plants in this group, for example, horsetail, have rhizomes modified into tubers, which serve both for the deposition of reserve nutrients and for vegetative propagation.
Horsetails reproduce mainly by rhizomes, forming many twin daughter plants, especially in places with disturbed vegetation, for example, after fires. Vast thickets of these weeds form in pastures and fields that are difficult to eradicate. Acid soil is favorable for the growth of horsetails, where they grow especially quickly and serve as a kind of indicators of soil acidity.
Horsetails are also characterized by reproduction by spores, which are contained in sporangia on sporangiophores. The stem contains spore-bearing zones of sporangiophores or they are packed into strobili at the apex. The gametophyte, or prothallus, looks like a small, short-lived unisexual or bisexual green plant. Also, the gametophyte may have the appearance of a brownish-pink, non-branching shoot, which dies after sporulation. On these growths there are antheridia with spermatozoa and archegonia with eggs. Water is required for fertilization to occur. The resulting zygote gives rise to a sporophyte.
Horsetails are widely used in folk medicine, in particular, horsetail preparations. These drugs are effective for hypertension, gout, and as wound healing agents. Horsetail fertilizer is used to supplement the nutrition of cows and goats to increase milk yield. Many wild animals eat horsetails. Some species of these plants, such as horsetail, are poisonous to farm animals.
The shoots of horsetails have a segmented structure, consisting of nodes and internodes. The leaves are collected in whorls.
Equisetaceae include both herbaceous plants (living and extinct) with a stem from several centimeters to several meters, and tree-like plants (only extinct), reaching 15 m and a diameter of more than 0.5 m.
The conducting system of the stem of horsetails is the actinostele or arthrostele. Most horsetails are homosporous plants, and only a few fossil forms were heterosporous.
The horsetail division unites two classes: wedge-leaved (Sphenophyllopsida) And horsetails (Equisetopsida).
Previously included in the class Hyeniaceae with representatives protohyenia (Protohyenia), hyenia (Hyenia, rice. 25 ) And Calamophyton (Colamophyton) are currently considered by paleobotanists to be the oldest cladoxylic ferns. In Kalamaphyton, the previously described jointed shoot nodes turned out to be simply transverse cracks in the rock. The anatomical structure of the hyena is still unknown, and the spore-bearing organs of both species rarely differ from the sporangiophores of Devonian horsetails (Meyen: Elenevsky et al. 2000).
CLASS EQUISETOPSIDA
The class Equisetaceae contains the order horsetails (Equisetales), families Calamitaceae (Calamitaceae) And horsetails (Equisetaceae).
Extinct representatives are united in the calamite family. Species of this family were widespread in the Carboniferous and then, together with lepidodendrons, sigillaria, ferns and cordaites, formed forests that produced coal deposits.
In appearance and structure, calamites resembled modern horsetails, but differed from them - they were trees, reaching a height of 8-10 m and even up to 20 m. Among them were both homosporous and heterosporous species.
The horsetail family includes one genus horsetail (Equisetum) and 25 species. There are 8 species of horsetail growing in the Republic of Belarus. They are found in swamps (E. palustre, E. fluviatile), in forests (E. sylvaticum), in bushes (E. hyemale), in meadows, fields (E. pratense, E. arvense), etc.
Modern horsetails are small herbaceous plants 80-100 cm tall, 2-5 mm thick. The tropical South American E. giganteum reaches 10-12 m in length and is a vine.
Horsetail consists of a rhizome located horizontally in the soil, from the nodes of which thin roots extend and above-ground shoots rise upward.
The stem of horsetail is segmented, ribbed, and consists of nodes and internodes. The internodes are hollow in the middle, the nodes are filled with parenchymal tissue.
The leaves of horsetails are scale-like, brown, devoid of chlorophyll, fused at the bottom into a tubular sheath attached to a node. Due to the reduction of leaves, the function of assimilation is performed by green shoots and stems. The branches are arranged in whorls, piercing the sheath of fused leaves.
In a cross section, the stem has the following structure. The outside of the stem is uneven, there are elevated areas (ribs) alternating with hollows. The outside of the stem is covered with a single-layer epidermis impregnated with silica, which gives it strength. Inside the epidermis there is a cortex and a ring of small, isolated conductive bundles of the collateral type with carinal (from the Latin carina - keel, ridge) canals. In the center of the stem there is a cavity at the site of destruction of the core. Under the ribs there are areas of mechanical tissue, and under the hollows there are assimilation tissue and vallecular (from the Latin vallis - valley, hollow) cavities. Under the mechanical tissue (under the ribs) there are vascular bundles of the collateral type, closed, without a cambium. In the epidermis, above the assimilation tissue, there are stomata.
Sporiferous spikelets of horsetails appear one at a time at the top of the main shoot, and sometimes on the lateral branches. In most species, the spore-bearing shoot is green. Aboveground shoots in some species can combine two functions - spore-bearing and vegetative. Yes, y horsetail (E. palustre) And riverside, or melted (E. fluviatila), vegetative and spore-bearing shoots arise simultaneously and do not differ morphologically from each other. Only in mid-summer do strobili form on some green shoots. In other species, separation of shoot functions is observed. Yes, y horsetail (E. silvaticum) And horsetail (E. pratense) in spring, simultaneously with vegetative shoots, non-branching, colorless or pinkish spore-bearing shoots develop. But after sporulation they turn green, branch and do not differ from vegetative shoots. In some species, shoot dimorphy is very clearly manifested.
Horsetail has two types of shoots. In the spring, brown, spore-bearing shoots grow from the rhizome, bearing one spikelet. The horsetail spikelet consists of numerous sporangiophores collected in whorls on its axis. Sporangiophores consist of a stalk and a corymbose hexagonal disc. On the underside of the disc, around the stalk, there are 5-13 sac-like sporangia. A large number of identical spores are formed in sporangia (unisporous). The spore has three shells: endosporium, exosporium and the outer layer of the shell, which cracks when ripe to form two hygroscopic ribbons around the spore, called hapter, which are attached to the spore in the center. In dry weather, they unwind like springs and help loosen the spores. In this case, the hapters of neighboring spores cling to each other. As a result, loose lumps of spores spill out from the sporangia and are easily carried by the wind. The growth of horsetail looks like a green plate, and in thickened crops or in water it looks like a green thread. The single-layer plate, growing, turns into a multilayered outstretched cushion with rhizoids on the underside. On the upper side of the pillow, vertical lamellar blades develop, on which the genital organs are formed. The size of gametophytes in different species varies from 1 mm to 2-3 cm. Within a species, male gametophytes are smaller than female ones.
Some species of horsetail are physiologically heterosporous.
In the best conditions of moisture and lighting, larger shoots (female) develop from the spores; in worse conditions, small shoots (male) develop.
The antheridia of horsetails are immersed in the tissue of the growth. Up to 100 multiflagellate sperm develop in them. Archegonia with a neck rise above the thallus. Fertilization occurs in damp weather. The embryo does not form a suspension and consists of a stalk, 2-3 leaves and a root.
After the spores fall out of the spicate strobium of horsetail, the spore-bearing shoot dies. New green, highly branched summer shoots grow from the rhizome.
The practical value of horsetails is small. The stems contain silica and are therefore used for cleaning metal utensils and polishing wood. The nodules on the rhizome of horsetail are sometimes eaten (contain starch). Some of the horsetails (field horsetail, meadow horsetail) are weeds. Some are poisonous (horsetail).
Rare relict species are included in the Red Book of the Republic of Belarus - horsetail (Equisetum telmateia) And variegated horsetail (E. variegatum).
What are the structural and reproductive features of horsetails (horsetails)?
Horsetails are perennial herbaceous plants with a segmented structure. The shoots are divided into nodes and internodes. The leaves are reduced to whole small blades. The function of photosynthesis is performed by the stem. Silica accumulates in the cells of horsetails, which makes the stem stiff. Horsetails reproduce by spores that form in spore-bearing spikelets. Spore-bearing spikelets are formed either on special spore-bearing shoots (in horsetail) or on the tops of vegetative shoots (meadow horsetail, wintering horsetail). The sporiferous spikelet consists of an axis on which sporangiophores are located. The sporangiophore consists of a stalk on which there is a hexagonal plate. On the underside of the plate there are sporangia. Spores are formed in sporangia. In dry weather, the spores spill out. A gametophyte (prothallus) is formed from the spore. It contains antheridia with sperm and archegonia with eggs. After fertilization, a zygote is formed, and from it an embryo and a new plant develop.
Mosses, horsetails, and ferns represent a group of the first land plants. Despite the fact that they arose more than 400 million years ago, these plants have become quite widespread in the modern period. The structure of mosses, horsetails and ferns, the features of their life activity and biological significance will be discussed in our article.
Plants coming to land
There is a theory that all living organisms, including plants, arose in an aquatic environment. The first of these were algae. Over time, environmental conditions have changed significantly, and the algae have had to adapt to endure long periods of drought. As a result, they gave rise to the first land plants. Even in the school botany course, ferns, horsetails, and club mosses (grade 6) are considered as land-dwellers.
The extinct group of the first land plants are representatives of the rhyniophyte division. Their low shoots were devoid of leaves and had forked branches. And instead of roots, rhinophytes had rhizoids, with the help of which they attached to the substrate.
Mosses, horsetails, ferns - higher spore plants
Modern spore plants have a more complex and advanced structure. Moss mosses, horsetails, ferns, like all representatives of this systematic group, are formed by real tissues. Thanks to their appearance, it became possible for plants to reach land. Tissues form organs: root and shoot. This is their main difference from lower plants, which consist of unspecialized cells.
Reproduction of these organisms occurs with the help of asexual reproduction cells - spores. Once in the soil, they germinate.
Life cycle concept
All higher spore plants have a complex life cycle. This is the period between two identical phases of development. It is he who ensures the continuity of life of a certain biological species. In the life cycle of spore plants, there is an alternation of generations - sexual and asexual. Sometimes they differ from each other in appearance.
The plant on which the spores form is an asexual generation. It is predominant in bryophytes. From the spore, an individual of the sexual generation grows - a gametophyte. The main differences between mosses, horsetails and ferns are in its predominance.
Let us consider each of the divisions of higher spore plants in more detail.
Department of lycophytes
They are evergreen herbaceous plants that grow in damp places. In most cases they are perennial. Moss mosses have creeping stems that branch in a forked manner. Small leaves are attached to them in a spiral.
The root system is formed by additional roots extending directly from the stems. In the area of the tips of the shoots there are scales, which are modified leaves. They contain organs of asexual reproduction - sporangia.
Features of the structure of horsetails
Modern horsetail species are also perennial herbaceous plants. Their characteristic feature is a clear division of the shoot into nodes to which tooth-like leaves are attached. At the base they grow together, forming a kind of vagina. The nodes contain cells of educational tissue, due to which the intercalary growth of horsetails in height occurs. The underground organ of horsetails is the rhizome, also divided into internodes. The function of photosynthesis in these plants is performed by the ribbed stem. Inside it there are many cavities filled with water and oxygen.
Horsetail sporophytes are green shoots that look like small young pine trees. And the gametophyte exists separately and looks like a green plate. One of the most common species of this department, horsetail, has two types of shoots. The first is also called spring, it is not capable of photosynthesis and bears spore-bearing spikelets. Summer, green, vegetative.
General characteristics of ferns
How do ferns differ from horsetails and mosses? The answer is obvious. This department is the most numerous and diverse, and its modern representatives have a more complex structure compared to horsetails and mosses. Among the 10 thousand species growing at this time, there are herbs, shrubs, and trees.
The group of homosporous ferns is represented by aquatic inhabitants - this is Salvinia floating and They freely float on the surface of reservoirs with a slight current. In the tropics, the Azolla aquatic fern is common, which forms a symbiosis with cyanobacteria that can absorb atmospheric nitrogen.
Heterosporous ferns grow in moist and shady forests. Their typical representatives are common bracken, male shieldweed, and other species.
It is about such plants that there is an amazing legend that a fern flower found on the night of Ivan Kupala will be endowed with an amazing gift - it will learn to understand the language of all living creatures. However, from a biological point of view this is impossible. Higher spore plants, including ferns, do not produce flowers or fruits.
How does a person use horsetails, mosses and ferns?
Higher spore plants have long occupied their niche in nature and human life. Ferns are part of a large number of plants used to create landscape decorations and as medicinal plants. But the most important role of these plants in nature is the formation of a valuable mineral - coal.
In ancient times, all spores were giant trees. Dying, their trunks, under conditions of lack of oxygen and high pressure from the layers of the earth, turned into coal.
How a person uses horsetails, mosses and ferns can easily be illustrated using the example of medicine. All of them are valuable medicinal plants. For example, horsetail has a hemostatic and diuretic effect. One of the representatives of the lycophyte department - - is used as a means to combat alcoholism.
The spores of these plants have long been used to make pyrotechnic products. In the pharmaceutical industry, club mosses are also used to coat tablets and make baby powder.
The main significance of higher spore plants lies in the fact that this valuable mineral has long been an important source of energy, since its combustion releases a large amount of heat. The electric power industry of many countries is based on this raw material.
Thus, mosses, horsetails, and ferns represent a group of higher spore plants, which is widely represented by fossils and ancient species. They are the first to land on land, which became possible thanks to the appearance of more progressive structural features: tissues and organs.
General characteristics of horsetails
One of the names of these very ancient plants is articular - very accurately characterizes the features of their structure. Equisetaceae shoots consist of clearly defined stems with internodes and nodes with whorled small scale-like leaves located on them.
It is these stems that make living horsetails and fossil species different from all other non-family higher plants and are a little like algae (characeae), gymnosperms (ephedra) and even flowering plants (casuarina).
Horsetail-shaped, as if assembled from construction kit parts, “jointed” plants, stand out noticeably against the background of grass in a forest, meadow or field.
Latin name for horsetails equisetophyta owes to the ancient Roman naturalist Pliny the Elder. He found some similarity between the branched shoots of horsetail and the tail of a horse ( equius - horse, saeta, seta- bristle).
In many European languages, the name horsetail is also translated as “horse tail.” For example, the Polish name sounds like konsciogon, English - horsetail and French - queue - de cheval.
In Russian title horsetail Echoes of cognate words also appear - “tail”, “horsetail”. In some regions of our country, certain types of horsetails with green, whorled leaves have been given names Christmas tree, pine. A pestles, pushers people call the spring generation horsetails - brownish-yellow spore-bearing shoots.
Ancient ancestors of horsetails - calamites- were huge trees, up to 20 m high, with powerful branched and ribbed trunks and looked like giant horsetails (see textbook illustration, p. 59). During the Carboniferous period, calamites, together with tree-like mosses and ferns, formed entire tiers of swampy tropical forests.
Giant dragonflies and other insects, which at that time were the only rulers of the air element, fluttered between the trunks; Ancient amphibians, the first conquerors of the earth's land, moved clumsily along the ground.
Modern representatives of horsetails are perennial rhizomatous herbs. Among them there are small, dwarf species and many rather tall plants. U horsetail The height of the stems is 5–15 cm, and their diameter is 0.5–1 mm. Stems of another type - horsetail polychaete reach 9 m, and the diameter is 0.5–2 cm. Such tall and thin stems with insufficiently developed mechanical tissue cannot independently remain in an upright position, so they grow relying on other plants.
Horsetails grow two types of stems: green vegetative and spore-bearing, chlorophyll-free, which quickly die. Both green and non-chlorophyll shoots have longitudinal grooves and are divided, like rhizomes, into nodes and hollow internodes.
From the nodes emerge whorls of branches and many small, often scale-like leaves, which grow together into tubes enveloping the stems. The scale-like leaves of spore-bearing shoots are chlorophyll-free. Sporangia are formed at the tips of the strobili.
The spores produce a very small green gametophyte, only a few millimeters in size. On the surface of such a tiny green plate, fertilization occurs only in the presence of moisture, after which a new generation, the horsetail sporophyte, develops from the united cell - the zygote without a resting period.
Horsetails are distributed very widely, almost throughout the globe, except Australia, growing in a wide variety of plant communities and zones, but always near water. These may be areas with sufficient moisture content in the soil or with relatively shallow groundwater.
Another characteristic feature of the growth and development of horsetails is their abundant growth over large areas as a result of vegetative propagation of even a single horsetail specimen. From the rhizomes of such a “father” or “mother” of all future vegetative descendants, more and more new shoots grow, which in turn develop new rhizomes with new shoots. So large stands of horsetails are often clones of the same plant and share the same hereditary properties.
In the formation of flora, the plant cover of our planet, at present, horsetails, like lycophytes, are not of great importance. The role of horsetails can even be negative. Rapidly multiplying in places with disturbed vegetation, horsetails become difficult to eradicate weeds of pastures and fields. Horsetails grow quickly even after careful weeding in fields and gardens, because on their well-developed rhizomes there are special formations in the form of underground tubers, which are called ground nuts or ground cones. Thanks to these features, horsetails also survive forest fires.
For the most part, horsetails are inedible for animals. Moreover, feeding horses hay with a large amount of horsetails can cause a disease that is popularly called “crank” or “drunken disease.” This disease manifests itself in paralysis of the legs and impaired movement of horses.
But wild boars and deer sometimes feed on horsetails in the fall and winter (they don’t eat them in the summer); apparently, the activity of toxic substances in wilted and frozen horsetails is significantly reduced.
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